26 August 2023

The Most Important Amplifier In Ham Radio

The title is a pretentious joke, but there is a kernel of truth in there.

A few days ago I wrapped up my HobbyPCB HardRock50 amplifier build, and I'm in the process of testing it with a variety of QRP rigs. So far so good with the Yaesu FT-818 and the Icom IC-705, and testing with the Elecraft KX2 is coming up. Right now I'm updating the external interface for the IC-705 that is manufactured by HobbyPCB, an interface that allows the amplifier to follow band changes on the radio and trigger tuning cycles

Earlier today I created a video showing the start-up procedure when using the amp and the IC-705 interface with the IC-705. The video shows how the IC-705 interface controls band switching (via Bluetooth), tuning and amp triggering. The interface works quite well, but it is an extra cost item ($70 as I have it configured) from HobbyPCB. Note - you DO NOT need this interface to run the IC-705 with the amplifier - the interface just takes care of the band switching and tuning duties, something you can do without the interface. You just have to do those tasks manually, and it's not at all difficult. 

I'm quite happy with the output. Signal reports from fellow hams are good, and I'm easily getting 50 watts PEP on sideband when driving the amp with 3 watts of output from the radio.

Building this amp was, as it's popular to say today, 'a journey', and I've outlined much of it in earlier postings. This is the second of these amp kits that I've built, and I learned a LOT on the first build. The reason I built this new amp is because the previous amp kit was an early model (shipped in 2014 but never built) and it had some issues regarding the ability to interface with the IC-705. I figured I'd start with a clean slate (and somewhat improved soldering skills) with a current production kit from HobbyPCB that included the internal tuner board. While this is not a tough kit to put together, it took me several months to get it done as work, family commitments and other factors got in the way. 

One of the hiccups was a blown capacitor on the amp board, which the manufacturer put down to it being a tantalum cap with known tendencies to let out the smoke when voltage is first applied. Jim Veatch, the owner of HobbyPCB, said they are likely going to switch capacitor types on the next production run. He cheerfully sent me two replacement caps. The job to replace them gave me the convenient excuse to buy a hot air re-work station to get the remains of the old cap off the board, get things cleaned up and the new cap in place. 

Luckily the damage was limited to the blown capacitor

Getting set to replace the blown capacitor

Another issue was the maddening discovery that the mounting holes for the tuner board had been mis-drilled in the case - basically they were drilled 'backwards', but you don't immediately know that until you go to mount the tuner board in the case and button everything up for testing - it just doesn't fit, and too much forcing can result in some bent connector pins (don't ask me how I know...). Again, Jim at HobbyPCB got back with me and let me know that their recent production runs had the holes on some of the cases drilled improperly, and he's only finding them when people like me bring up the issue. He offered to replace the case but I had to ship the old one to him first, or he could send me a template that would allow me to drill my own holes in the proper location. I opted to go the template route.

So, I can't emphasize too much that this is a 'hobby' build - the instructions are very good, and on-line support is good (Jim answers emails promptly and very courteously), but you are still likely to run into glitches like I did. This is where the hobby aspect comes into play, and you're kind of expected to do your own troubleshooting. Adversity builds character, right? But HobbyPCB also states that the price of the kit includes a working amplifier, so if you get it all together and simply can't get it working you can ship it off to Jim and he'll diagnose and fix whatever's wrong, for free.

The IC-705 interface module - a box that connects between the amp and the 705 and allows
automatic band switching and tuner operation. It's basically an Arduino board with a Bluetooth
interface. I just got through soldering in the add-on board that drives the tuner in the HardRock50
(the lighter colored board in the upper right)

Another challenge for those of you not used to running bootloaders is updating the firmware. Your kit will likely ship with a slightly outdated firmware version. Updating the firmware isn't tough, but you have to install a bootloader on your computer and run the update from there. It's a well documented procedure, but might put off those with limited computer skills.

Last, although everything about this amp and the add-on components like the tuner and control interface are well documented, the HobbyPCB website is something of a dog's dinner in terms of organization, and HobbyPCB has some dead links and pointers to outdated files out there. They need the help of a good web developer.

So what's the use case for this amp? For me it's simply this - with the demise of portable all-band, all-mode 100 watt rigs like the IC-7100 or the FT-857, I am looking for more 'oomph' for both my IC-705 and my KX2. I love those rigs, but feel that they are limited by their 10 watt output, particularly when working voice. Let's focus on the IC-705 - an incredibly capable radio that brings together all the features anyone would need for portable operations. I consider 50 watts as something of a sweet spot for portable work. In most cases going from 50 - 100w output doesn't really get you much beyond greater power consumption. I also like the idea of the two components in separate packages. If I only want to run digital I can go out with just the radio and work at 10 watts. If I want to run voice, I can bring along the amp and push things up to 50 watts. With the internal tuner in the amp I can also leave the Icom tuner behind. It's all about options and capability.

OK, what about this silly 'most important amp in ham radio' claim? Well, here's the truth of it. To be an effective portable shack-in-a-box radio the IC-705 needs to put out more than 10 watts. This is particularly important if you want to use the rig for EMCOMM applications. Ten watts may be enough for digital modes, but for SSB it's not enough for reliable & repeatable comms. There are a number of solid state amps on the market that will work with the IC-705, but they generally fall into two categories - low cost, low output Chinese manufactured amps of poor quality, and high quality (and expensive) 100+ watt amps designed for in-shack use from companies like Elecraft, RM, ACOM and others. The HardRock50 is the only high quality, field portable, well supported and reasonably priced amp available for QRP rigs. This means the HardRock50 stands alone as an amplifier that can turn the IC-705 into a serious field radio for EMCOMM use. So while not the most important amp in all of ham radio, it is still the best option to turn your field QRP rig into an effective tool for reliable communications.

The next step is testing using a battery instead of a power supply - I'll test using a 12 amp hour LiFePo battery to see how long that holds up in field use. I'll also be testing with the KX2. So stay tuned!

W8BYH out

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